Electrophysiological analysis of brainstem neurons subserving autonomic and motor oral functions

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Neural network in the brainstem subserving autonomic and motor oral functions was investigated by electrophysiological and behavioral studies. In the electrophysiological study, biophysical properties of the superior salivatory (SS) neurons were analyzed by the whole-cell patch clamp technique in sliced brainstem preparations. Neural activity of the trigeminal motor neurons were also analyzed by the intra-cellular recording technique in sliced preparations. The SS neurons innervating the tongue displayed a prominent transient outward current (A-current), and fired up to 70 Hz. Those innervating the salivary glands expressed A-current lasting longer period, and fired up to 30 Hz. The SS neurons innervating the different targets scattered and intermingled in the lateral reticular formation of the medulla oblongata, which have 3-4 main dendrites that extended dorso-ventrally about 700 μm. The two kinds of SS neurons showed similar whole cell currents which of some neurons were antagonized by picrotoxin, 2-amino-5-phosphono-valeric acid (AP-5) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), suggesting that major components of the postsynaptic currents could be mediated by GABA_A-. NMDA- and non-NMDA-receptors. In behavioral study, salivary flow from the submandibular gland and activity of the masseter muscle were chronically recorded from the freely moving rats. During chewing. the amount of saliva and muscle activity were always parallel. When emesis was yielded by intravenous injection so apomorphine, salivary flow rate was correlated with movement of the stomach, but now with jaw movements.Through these studies, we conclude that the central nervous system integrates the autonomic and motor oral functions, and it is likely that a contact point between the two functions is situated in the lower brainstem especially the lateral reticular formation. The activity of the pre-motor neurons of the trigeminal motor nucleus should be analyzed in a new research project.